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Imperial PA (Read 8172 times)
DirtDawg
Ex Member



Re: Imperial PA
Reply #15 - 09/19/05 at 13:14:50
 
To full range or not to full range? There are tradeoffs to consider, as mentioned by stv.

If you run them full range they will probably sound more "live" and open, at times, but less controlled, great for drums, not so good for acoustic guitar and voices. The 15's will start to beam noticeably around 800Hz and serious (objectionable) combing in relation to the horns starts from 2K-ish range and up to where ever the 15's roll off significantly. Beaming is more of problem outdoors, combing is worse indoors. Beaming becomes much less noticeable with a PA on the short side of a long skinny room, except up close, of course, but you probably don't want to be very close to them for your ears' sake. Combing in the same room is much worse. If you are going for a HiFi sounding clean, flat, non resonant response, you need to cross them before they start to beam. That solves both problems, except for any combing caused by the 2 - 15's side by side. To fix that you need to cross much lower, like 150Hz range depending on how far apart they are, but combing in that range seems to be less noticeable to most people. The best way to detect and correct for either is to use pink noise (download to laptop) and move around a little.

When running an amplifier in mono mode you don't get more power. The main advantage to bridging for mono is in impedance matching and sometimes increased (percieved) headroom. Pretend for a moment that amps are perfect and you have 2 X 500W @ 8 ohms (stereo), in mono you will still have 1000W (2 X 500) but, the amps impedance is 16 ohms now. With 4 - 8 ohm drivers using stereo you can put 2 drivers across each side in parallel, and get 2000W total, in mono you usually can't drive a 2 ohm load so you put your drivers in series/parellel giving you 8 ohms again and the output is 2000W. If you try to run 4 ohms in mono (or 2 ohms in stereo), unless it is specifically designed with that possibility in mind, which many are nowdays, you will either be hitting the thermal limits of the amps, which means it takes a nap if you're lucky, or severely compresses the signal to protect itself.
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« Last Edit: 09/19/05 at 13:25:01 by DirtDawg »  
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Corey
Ex Member



Re: Imperial PA
Reply #16 - 09/19/05 at 17:12:58
 
What do you recommend fro a x over to do both jobs, like in one box?

I am only familiar with car audio xovers like Audiocontrol 24XS etc.

Corey
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DirtDawg
Ex Member



Re: Imperial PA
Reply #17 - 09/19/05 at 22:32:30
 
[quote author=Corey  link=1126582246/15#16 date=1127146378]What do you recommend fro a x over to do both jobs, like in one box?
[/quote]

I'm not clear what you mean by "both jobs". I have used Crown, Rane, Yamaha, Ashley, even the cheapest, DOD crossovers, and Rane, Yamaha, Ashley, and UREI equalizers (a 1/3 octave EQ on each channel is handy Smiley) with good results.
Bargains are out there, and I would grab any one of these brands if I could get it for a song or two*, but I wouldn't buy anything new without first checking out the Behringer DCX2496 Crossover.
I haven't used these, but to me it seems like a tremendous value. I've heard hot and cold about this unit on other forums. Maybe some of our resident smart guys who has one can weigh in on this idea. Are you building a 2-way, 3-way, 4-way?


http://www.behringer.com/DCX2496/index.cfm?lang=ENG

* A DOD would have to be very cheap, like <$40 to be a bargain in my opinion.
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« Last Edit: 09/19/05 at 22:36:00 by DirtDawg »  
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stvcmty
Ex Member



Re: Imperial PA
Reply #18 - 09/20/05 at 00:24:33
 
Running an amp bridged mono into a 4ohm load [2 8ohm loads in parallel] produces more power than running it stereo into 2 separate 8ohm loads.

I would never buy an amp that was not 2ohm stereo stable unless the price was 50% less than normal retail.  The flexibility that 2ohm stereo stable amps give is worth paying more for them in the short term.

The distinction I was making is using a single RMX5050 would be better than using 2 CE2000’s.  The reason is dampening and wasted power.

I really like the Behringer CX3400 crossover.  Combined with a decent 31band graphic EQ, it can take care of just about anything.

Look at the response graphs for a GW15120 on parts express.  Its response falls really fast, so it should not be terribly bad about beaming/comb filtering if it is used with something else in an imperial.

The difference in the front radiation sensitivity between a Peavey black widow HE and a GW15120 would also help to prevent comb filtering.  The main purpose of the GW15120 in the imperial is back loading into the horn.  The Black Widow HE is strong enough to back load into the horn well, but it is also sensitive enough so the front radiation keeps up with the horn.

One thing I would not do, run the imperial as a 3 way cabinet.  Both 15” speakers need to be fed bass, they are in the imperial’s compression chamber to feed the horn.  I could see having an active roll off for one of the drivers between 90 and 150hz, but the other one would need to either be full range, or crossover to the Compression Driver/Horn.

Stv
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DirtDawg
Ex Member



Re: Imperial PA
Reply #19 - 09/20/05 at 02:59:35
 
Quote:
Running an amp bridged mono into a 4ohm load [2 8ohm loads in parallel] produces more power than running it stereo into 2 separate 8ohm loads.

I would never buy an amp that was not 2ohm stereo stable unless the price was 50% less than normal retail.  The flexibility that 2ohm stereo stable amps give is worth paying more for them in the short term.


stv,
You and I are not in disagreement. We are both saying the same thing 2 different ways.
Corey, keep in mind the fact that many of the bargain priced top brand amps out there are not the newer models with 2 ohm stereo or 4 ohm mono capabilty, so just be sure which model # you are looking at before you buy.


Quote:

One thing I would not do, run the imperial as a 3 way cabinet.  Both 15” speakers need to be fed bass, they are in the imperial’s compression chamber to feed the horn.  I could see having an active roll off for one of the drivers between 90 and 150hz, but the other one would need to either be full range, or crossover to the Compression Driver/Horn.



Absolutely right and I would send the same signal to both 15s and not worry too much about combing between them. You can't overlap the 15s and the horns and expect to get a flat response, so get that range out of the horns. I didn't see a polar response graph on either driver, but you have to decide how much beaming from your 15s you can tolerate, anyway. My tolerance is zero, so I would cross any 15 over at around 800-1500 Hz, but that's possibly @n@l if you only need 30degrees mid dispersion.
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stvcmty
Ex Member



Re: Imperial PA
Reply #20 - 09/20/05 at 03:36:34
 
http://www.partsexpress.com/pdf/290-397b.pdf

For the Goldwood, scroll down to page 3.  It doesn’t give polar response, but it does show the gold wood peaks at about 125hz and falls quickly above that.

The horn will load the rear of the driver, getting bass from it, but the front radiation will be seriously drowned out by a higher sensitivity driver.

I think this site has the GW15120 on clearance, http://www.cheaplights.com/catalog/01_info.php?sec=411
I ordered the 411-WF1558 from them and it was a gold wood 1558.

Stv
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stvcmty
Ex Member



Re: Imperial PA
Reply #21 - 10/01/05 at 23:25:58
 
I don’t think I can recommend a QSC RMX5050 now.

I went to guitar center today to trade in some speakers, and before they would take them, they had to test them.

They used a RMX5050, and I was not impressed.  I have used a CE1000 bridged mono with the speakers I was trading in, and that combination would bring down the house.  They bridged mono the RMX5050 against the pair of speakers, and it sounded bad.  At low volume it distorted.  I thought the person testing them didn’t know what he was doing, but I checked the source, the board, and the crossover, and they are all correct.  The RMX5050 went into protection mode for no good reason several times.  The guy thought it was my speakers [it wasn’t, I tested them this morning, and they work fine] so he tried hooking up a set of JBL speakers, and they sounded just as bad.

It may be that it was a display model, but my “hands on experience” with the RMX5050 is not so good.  The online reviews I have read of the RMX5050 are good, but there is a difference between reading about something and experiencing it.

Then we tired testing the speakers I was selling on a CE4000, and everything worked fine.  So if I had to pick a high power amp, I would go with a CE4000.

Stv
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stvcmty
Ex Member



Re: Imperial PA
Reply #22 - 10/02/05 at 00:09:02
 
Why must so much of sound come down to the differences between spec sheets and real life?
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Braggi
Ex Member



Re: Imperial PA
Reply #23 - 10/05/05 at 04:09:04
 
I'm pretty happy with my CE1000. It's noisy if I don't use a balanced preamp though.
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stvcmty
Ex Member



Re: Imperial PA
Reply #24 - 10/05/05 at 05:14:25
 
I run 2 CE1000’s, but some times, I need more power, which is no fault of the amplifiers.

The RMX5050 is one of the largest cost effective amplifiers I have seen, which is why I was interested in it for a while.

The largest pro sound amplifier I have seen is a Crown IT8000.  4000 watts per side into a 4ohm load.  It just ends up being about $1 a watt.

After my experience with the qsc, I will be staying with crown amplifiers.  The CE1000 is a safe bet, always.

Stv
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DirtDawg
Ex Member



Re: Imperial PA
Reply #25 - 10/05/05 at 05:14:46
 
Most of the DJ rigs I've seen are not balanced, at least not really because, so many effects rack toys unbalance at the inputs. If you're running very many live mics, you need to go balanced all the way to the power amps, or you will hear every lighting ballast up a block away or more. ???
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DirtDawg
Ex Member



Re: Imperial PA
Reply #26 - 10/05/05 at 05:20:03
 
[quote author=stvcmty  link=1126582246/15#24 date=1128485665].....  It just ends up being about $1 a watt.
Stv
[/quote]
It sounds pretty cheap when you put it that way. Grin
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stvcmty
Ex Member



Re: Imperial PA
Reply #27 - 10/05/05 at 05:33:24
 
Not when it is an 8000-watt amp and tuition is $12,000 a semester…

Balanced gear is good.  Having a separate hot and cold line is nice, because the signal ground can be lifted to get rid of hum.

Speaking of balancing, hum, PA’s and grounding, is there any safe, easy way to setup a temporary star ground for a show?

Stv
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DirtDawg
Ex Member



Re: Imperial PA
Reply #28 - 10/05/05 at 06:49:38
 
I always ran a separate ground from my board to my power mains rack, kind of "star" like. Everything grounded to the mixer, and out thru a cable separate from the snake. If I needed to lift a ground I would use an "adapter" ( 1 foot mic cable without the ground connected, spray painted orange ) at the mic end. I had a doctors bag ( actually a tenor sax case that weighed over 100lbs, nicknamed "The Dreaded" ) of impedance transformers, adapters of all kinds, and isolation transformers and all knids of cool stuff for hums. Nobody ever got shocked after I did the ground on the board, except for a couple of guitar players, but it was thier stuff, that bit them.
Here's a cool link full of info:

http://www.rane.com/note110.html

And another

http://www.gbaudio.co.uk/data/ground.htm

Oh, sorry, I forgot the "easy" part.    :)
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« Last Edit: 10/05/05 at 06:50:26 by DirtDawg »  
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Papi_Bill
Ex Member



Re: Imperial PA
Reply #29 - 10/06/05 at 14:25:41
 
skip the dod and behringer crossovers, and  buy a dbx driverack pa. used at around $300 on evilbay...get the calibration mic too while you're at it... in one rack space you get up to 3 way stereo x/o with alignment delay, graphic and parametric eq, feedback suppression, compression, subharmonic synthesis (not sure if that would be useful with imperials though!) and limiters on each output. Oh yeah, the box will "auto eq" the room using pink noise and the calibration mic....
you would need to buy at least 3 or 4 of the above mentioned items for a reasonable pa anyway.... save space time and money and get one of these....  dbx makes grea stuff... I have one in use with my w/o pa...and the second on my bass rig for now until I build some monitors.
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« Last Edit: 10/06/05 at 14:27:19 by Papi_Bill »  
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